The tray index says Dad visited MIT in July 1953 and then had his 10th reunion summer 1961. Hayden was built in 1951. Some other slides with codes numerically near B46 were taken in 1956. More likely 1953, since slides with film mount Kodachrome red-on-grey, slide number, no month/year only go as late as 1960 (at least of the 5000 I’ve scanned so far).
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B45